Microbial biological control agents (MBCAs) are biological pesticides which are derived from microorganisms and have the potential to control plant pests and diseases. As the understanding of MBCA efficacy and the mechanisms which underlie MBCAs has improved, the application of MBCAs has been extended. For example, mild virus strains can now be used to facilitate the cross protection of crops. This study discusses and summarizes the data that is required to register mild virus strains in the United States, Europe, and Japan. Our findings can serve as a reference for the management of mild virus strains in Taiwan.